It never ends

[camper4lyfe]

I got almost home tonight and was stopped at a light. It felt as though the engine was surging, and the rpm's were fluctuating a little bit.

When I got home, I played around a little bit while sitting still. While in gear (any gear), the rpm's seemed fine. As soon as I dropped it into neutral or park, the rpm's dropped to about 500. When I put it back in gear, the idle would come back up to around 700.

I'm going to pull the IAC tonight and give it a clean to see if that makes any change. Anyone have any other thoughts?

I'm thinking I've got transmission issues (see my hiccup/stumble thread) as well, and I don't know if this is related or not. I'm about ready to drive this thing off a cliff.

For record, it's an 03 FX4 4.0L with an auto trans. with just shy of 97k.

 

[xentris02]

today i had the exact oppisite problem. my truck idles at 700 800 rpms in or out of drive and today i put it in drive and it dropped to 500 and stayed there till i started driving but while i was driving i noticed thats the rps were a little higer than normal (for how much i was pressing the gas) and the transmition seemed to not be puting out enough power the who ride home till the last stop light.

 

[camper4lyfe]

today i had the exact oppisite problem. my truck idles at 700 800 rpms in or out of drive and today i put it in drive and it dropped to 500 and stayed there till i started driving but while i was driving i noticed thats the rps were a little higer than normal (for how much i was pressing the gas) and the transmition seemed to not be puting out enough power the who ride home till the last stop light.

Have you checked your fluid level?

 

[low-keys89v6]

Im having a similiar problem as the OP. My truck runs great except for in Park and neutral. My IAC valve has been changed. Im thinking computer, brake booster or cat converter.

I agree with camper4lyfe on the fluid thing on the #2 poste and also check/change the screen possibly. Specially if it was ran low on fluid or if the fluid is just burnt. I have seen catalytic converters cause similiar problems. Feels like your towing a trailer when your not...worth checking. good luck

 

[camper4lyfe]

I'm bumping this thread rather than create a new one for the same problem.

For most of the year this hasn't happened, but has recently started acting up again. For some reason it seems to be ambient temperature related, though I'm not 100% on that. I thought it was transmission related, but I had it checked out and it's fine, though it needs a fluid change.

Just to recap, the truck starts and runs fine. The only problem I'm running into now is that when I drop into neutral or park from any drive gear, the rpm's drop to 500 or below, causing the truck to stumble a bit as the rpm's slowly come back up to where they should be. Every once in a while it'll stall, but it's rare. I haven't changed anything since the original post, aside from cleaning the IAC back in January. Oh, and the truck's up to almost 102,000 miles.

Maybe someone new will see this and have a suggestion?